We plan to investigate alterations in the biosynthesis of RNA in Salmonella typhimurium following infection by bacteriophage P22. We have, for example, obtained evidence that the rate of RNA synthesis transcribed from the host genome is reduced sharply following phage infection. First, we intend to study the time course of RNA synthesis post infection and to determine which species of RNA are affected, i.e., tRNA, rRNA or mRNA. We will use the techniques of RNA pulse-labeling and RNA-DNA hybridization. Second, we intend to isolate and characterize bacterial mutants which are altered in transcription and which at the same time affect phage development. More specifically, we will isolate RNA polymerase mutants (e.g., mutants resistant to rifampicin or streptolydigin) which alter phage development. The growth of wild type P22 as well as various P22 regulatory mutants will be tested on these host mutants. Both the physiological and biochemical properties of these RNA polymerase mutants will be studied. Finally, we intend to isolate and characterize P22 mutants which suppress the effects of the bacterial mutants. These phages may contain altered factors which interact with the host or with host-phage complexes at the transcriptional level. The affected gene and the altered gene product of these phages will be characterized. Studies on RNA synthesis after P22 infection and on phage and host mutants which affect RNA synthesis may reveal how the bacteriophage and the host interact at the transcriptional level.